Frequency Changer Research Articles

High Pressure Sodium Lamp High Power Factor Electronic Ballasts Using AC–AC Converters

Electronic ballasts usually present two stages, one for feeding the high pressure sodium (HPS) lamp and the other for power factor correction (PFC). This paper presents electronic ballasts using ac-ac converters without a PFC stage. The use of an indirect ac-ac converter, or an indirect frequency changer, to feed the HPS lamp is investigated. Modulation strategies are proposed to improve the input and output characteristics of the converter. Further studies lead to a novel HPS electronic ballast which uses an ac chopper capable of achieving PFC and supplying high frequency to the lamp. Different converter topologies, bidirectional switches, and a modulation strategy for the ac chopper are presented. Due to the output characteristic of both topologies, the lamp current is modulated at the frequency of the voltage source and the consequences of this operation are discussed. The experimental results for both electronic ballasts supplying 250-W HPS lamps are presented

A TERAHERTZ PHASE FREQUENCY CHANGER WITH THE CRYSTAL QUARTZ PHASE SECTIONS

A phase frequency changer (PFC) for quasi-optical transmission line with phase sections made of crystal quartz and polarizers executed on the basis of small-period wire gratings has been considered. The PFC is intended for operation in terahertz (THz) frequency region. It has been examined at the frequency f o= 0.89THz. The influence of the differential phase shift deviation in the sections on the output signal spectrum and the influence of the sections mismatch on the reflection signal spectrum have been considered. In the frequency region ± 10% f o the levels of the spurious spectral components of output signal are less than −40 dB with regard to the level of the useful signal of the shifted frequency. The levels of all spectral components of the reflection signal are less than −60 dB with regard to the level of the useful component of the PFC output signal.

Experiment on Fractional Frequency Transmission System

The fractional frequency transmission system (FFTS) is a very promising long-distance transmission approach, which uses lower frequency (50/3 Hz) to reduce the electrical length of the ac power line, and thus, its transmission capacity can be increased several fold. This paper introduces the experimental installation of FFTS and primary experiment results. The experiment uses the phase-controlled cycloconverter as the frequency changer, stepping up 50/3 Hz electricity to 50 Hz electricity and supplying it to the utility grid. Thus, a new flexible ac transmission system device is successfully established in this experiment. The synchronizing process of 50/3 Hz transmission system with 50 Hz utility system is introduced in this paper. The experiment results show that a 1200 km/500 kV transmission line can transmit more than 2000 MW electric power when employing the FFTS. The experiment also illustrates that there is no essential difficulty to realize FFTS in engineering practice.

Electrification of a major steel mill. Part III. introduction of 60-Hz power at Bethlehem works

The Bethlehem works of the Bethlehem Steel Company was one of the major integrated steel mills in North America and describes the introduction of 60-Hz power at the Bethlehem works. A frequency changer of the type installed for this purpose consists of two AC synchronous machines coupled together. This new frequency changer installation was a joint venture between the Bethlehem Steel Company and PP&L. Loop substation became the central power dispatching facility for the Bethlehem works.

The frequency changer era-interconnecting systems of varying cycles

At the start of the 20th century, the five different frequencies of 25, 30, 40, 50, and 60 cycles were in use, to a greater or lesser degree, in the United States. There was also a smattering of other oddball frequencies. As a result of the number of frequencies in use, the concept of the rotating "frequency changer" was developed early in the last century in order to be able to interconnect systems operating at two different frequencies. This article describes the development of the rotating frequency changer and its application, over the past century, in a variety of utility, industrial, and transportation power systems. In particular the induction-synchronous frequency changer is discussed.

Three-phase induction motor integrated with a magnetic frequency changer

The new solution of the high-speed induction motor model is presented. The basic structural part of the motor is magnetic circuit with non-linear elements in which the third harmonic of the flux is generated. The finite element method is used to solve the coupled equations for the magnetic field, the stator windings and conductors of the rotor.

The Power electronics handbook

Contents : Part 1 : Components : Power semiconductor devices. Thermal design. Power semiconductor control components. Electromagnetic compatibility. Power semiconductor protection. Part 2 : Circuits : Power semiconductors circuits- a resume. Static switches. AC line control. Phase-controlled rectification and inversion. Direct ac frequency converters. Forced commutation techniques. DC to dc converters. DC link frequency changers. Part 3: applications : Power semiconductor circuit applications. Smart power. Appendix 1: list of symbols. Appendix 2: glossary of terms. Bibliography. Index.

Fundamental operation of direct linked frequency changer with bilateral switching circuits

Fundamental operation of direct linked frequency changer with bilateral switching circuits

Direct-linked-type frequency changer based on DC-clamped bilateral switching circuit topology

This paper describes a direct-linked-type frequency changer (DLT-FC) proposed by the authors. The DLT-FC is a converter circuit with a new configuration for direct frequency change. The DLT-FC does not require a DC-link circuit, nor bilateral switches. In addition, DC snubber circuits can be applied without the need for a regenerative circuit of snubber energy. Therefore, the DLT-FC can be designed to be compact and lightweight, and have a long life. The authors made a prototype of the DLT-FC and experimentally checked its operation. The results indicate that the performance of the DLT-FC makes it suitable for industrial use.

Fundamental Operation of Direct Linked Type Frequency Changer with Bilateral Switching Circuits

This paper describes a direct linked type frequency changer (hereafter called DLT-FC) proposed by the authors. The DLT-FC is a converter circuit with a new configuration for direct frequency change. The DLT-FC does not require a dc link circuit, nor bilateral switches. In addition, dc snubber circuits can be applied without the need for a regenerative circuit of snubber energy. Therefore, the DLT-FC can be designed to be compact and light weight, and has a long life.The authors manufactured a prototype of the DLT-FC and experimentally checked its CVCF and VVVF operation. The results indicate that the performance of the DLT-FC makes it suitable for industrial use.

交直連系系統に対する最適潮流計算法の開発

Optimal power flow (OPF) is to minimize a certain objective function such as generation cost or transmission loss while satisfying various constraints posed from system operations and hence can be a powerful tool for making up reasonable operation plans. Since the advent of DC transmissions in mid 1950's, it has been used as a useful substitute of an ac transmission in cases of long distance transmission, transmission through marine cables, frequency changers, ac-dc parallel transmission, etc. Therefore, it is highly needed to develop an efficient OPF algorithm into which dc transmission systems can be integrated without significant modifications of an OPF program for ac systems. This paper presents an extension of the current Newton OPF program, which directly solves the Kuhn-Tucker conditions and is regarded as most efficient and robust at present, so that the OPF can incorporate dc transmission systems. The control schemes of a dcsystems have been satisfactorily integrated into the developed OPF algorithm. Numerical experiments on a test system have verified the effectiveness of the proposed algorithm.

Novel Three-phase SMR Converter.

We already developed a conventional SMR (Switch Mode Rectifier) converter using bilateral switch. A conventional SMR converter has a weak point that is to be need of AC snubber circuit and the complicated circuit for regeneration of snubber energy.This paper discribes a novel three-phase SMR converter which was named DC-Clamped type SMR ( DCC-SMR ) using direct frequency changing technology for industrial use power supply. DCC-SMR consists of frequency changer, HF (High Frequency) transformer and HF rectifier. Frequency changer of DCC-SMR doesn't use bilateral switch. Then, we can use DC snubber for switch. Furthermore, DCC-SMR doesn't-need regenerative circuit and discharge resistance, because snubber circuit is only capaciter and snubber energy is regenerated to primary winding of HF transformer by main switch.We verified usefulness in experimentation. Moreover, we refer to efficiency of 100kw prototype system.

Resonant snubbers with auxiliary switches

A resonant snubber is described for voltage-source inverters, current-source inverters, and self-commutated frequency changers. The main self-turn-off devices have shunt capacitors directly across them. The lossless resonant snubber described avoids trapping energy in a converter circuit where high dynamic stresses at both turn-on and turn-off are normally encountered. This is achieved by providing a temporary parallel path through a small ordinary thyristor (or other device operating in a similar node) to take over the high-stress turn-on duty from the main gate turn-off (GTO) or power transistor, in a manner that leaves no energy trapped after switching. >

Development of an optical instrument transformer for DC voltage measurement

This paper deals with the principles, design, assembly, testing results and practical application of a new type of optical voltage instrument transformer based on the Pockels effect, developed for the measurement of DC voltage, with a view to the protection and control of DC power transmission systems including frequency changer power equipment. In order to develop more accurate devices, the authors conceived a new scheme capable of overcoming the particular problems of DC voltage measurement which cause measurement errors. In this scheme, the DC voltage to be measured is chopped and applied to the Pockels crystal. An optical DC voltage instrument transformer was developed and tested using this scheme. The results of the factory tests showed that the characteristics of the new device conform with the required specifications of DC voltage instrument transformers for the protection and control of frequency changer power equipment. The results of field tests conducted for 1 year at an operating frequency conversion substation confirmed that the device is of adequate reliability. >

A new variable-speed AC generator system using a brushless self-excited-type synchronous machine

A new variable-speed synchronous generator system is proposed. The system consists of a brushless self-excited-type synchronous machine and a voltage source PWM frequency changer. In the generator, the field current is obtained by superimposing another field on the stator rotating field, which is achieved by control of the PWM converter so that AC voltages are induced and half-rectified in the rotor field windings. Neither an exciter nor additional exciting equipment is required for this generator. In order to superimpose the additional field on the stator field, two modulation schemes of the PWM converter of the frequency changer are given and the characteristics of this generation system are discussed on simulation and experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Direct frequency changer operation under a new scalar control algorithm

A thorough analysis of a scalar control method for the operation of direct frequency changers (DFC) using bidirectional switches operating at high switching frequencies is proposed. The method allows full control over voltage and frequency at the output port and the input side power displacement factor, with little effect on the frequency spectrum of either the output voltage or input currents. The method uses the instantaneous voltage ratio of specific input phase voltages to generate the active and zero states of the various switches. A voltage transfer ratio as high as 0.87 is obtained under synchronous and asynchronous operation with a conventionally connected three-phase load. Analysis shows that the input power displacement factor is independent of load characteristics. The power displacement can be precisely controlled by proper adjustments of the timing sequence. Synchronization error in the timing sequence affects both the input power displacement and the voltage transfer ratio. >

Analysis of ‘D type’ flip-flop frequency changers

A novel approach using Fourier analysis to model a digital system, in this case a ‘D type’ flip-flop, is presented. An analysis of the flip-flop using mathematics, with a graphical example to illustrate the logic operation of the flip flop as a frequency changer, in this case a down-convertor, is presented. This type of analysis could prove invaluable in modelling digital phase locked loops and frequency synthesisers.

Power electronics handbook: components, circuits, and applications

Part 1 Components: power semiconductor devices thermal design power semiconductor control components electromagnetic compatibility power semiconductor protection. Part 2 Circuits: power semiconductor circuits - a resume static switches A.C. line control phase controlled rectification and inversion direct a.c. frequency converters forced commutation techniques d.c. to d.c. converters d.c. link frequency changers. Part 3 Applications: power semiconductor circuit applications.

Characteristics of variable speed brushless self-excited type synchronous generator system.

This paper presents a variable speed synchronous generator system. The system consists of a brushless self-excited type synchronous generator and a bi-directinal voltage source PWM frequency changer. The rotor field windings of the generator are short-circuited with diodes, and the field excitation is obtained through the half-wave rectification of the induced voltages. To induce the AC voltages in the field windings which are rotating at synchronous speed, the stator output currents of the generator are so controlled by the PWM converter coupled to the generator that they can contain DC components. In addition, the rotating fields which are produced by harmonic components included in the stator current, are used effectively to obtain a self-excitation. The system can provide power generation into the power system over a wide speed range at unity power factor.In this paper, a simulation of the steady state characteristics of the generator is given, which takes account of both the resistance of each winding and the interruption of the rotor field current caused by the insertion of the diode, also the characteristics of the system are clarified through both the simulation and experiments.

Energy and hydrodynamic studies of turbine operating regimes of large pumping stations

1. The possibility of operation of axial-flow pump units in a turbine regime was proved experimentally. 2. To provide efficient operation of the PSs in pump and turbine regimes it is expedient to carry out double regulation by means of the runner blades and gate vanes. 3. The maximum efficiency values of the model of the PSs withD1=350 mm are 81.5% in the turbine regime and 86.0% in the pump regime. 4. The zones of the optimal efficiency values of the characteristics of the pump and turbine regime do not coincide by 20–25% with respect to the reduced rotational speed. For matching the operation of the unit in the optimal zones of both regimes it is recommended to use a static frequency changer. 5. The blade frequency, frequency of revolution, and low-frequency oscillations excited by the vortex line behind the runner are the dominant frequencies of the pressure fluctuation process in turbine regimes with maximum energies.